In numerous situations, when explosive devices are prepared, transported, or otherwise handled, small amounts (e.g., on the order of micrograms/cm2) of the explosive material, or related residues, can become disposed on surfaces. Such surfaces may include clothing, a container, a vehicle, the ground, window sills, and other substrates. Detection of such chemicals can provide a warning of possible concealed assembly and/or transport of explosive materials and devices.
While several methodologies have been developed to detect such materials, each suffers from deficiencies and/or disadvantages. For instance, x-ray transmission, x-ray backscatter, terahertz (THz) imaging and the like are sensitive only to bulk amounts of explosive material or metallic constituents in explosive devices; such techniques typically cannot detect very low surface quantities of explosive materials/residues. Ion-mobility spectrometry (IMS) requires surface sampling, for instance by airflow agitation, followed by collection of dislodged particles. Thus, the detection is relatively slow, and effective only at short distances (e.g., 1-2 meters). Raman spectroscopy has a very weak signature, requiring data collection for extended periods of time. Laser-induced breakdown spectroscopy (TABS) is prone to generating false alarms in many situations since it is largely non-specific, detecting atomic constituents which are found in many compounds (oxygen and nitrogen). Differential reflectometry is effective only from relatively short distances (˜1 meter), and is also prone to generating false alarms since its signature is complex and not well defined, fluorescence quenching (e.g., using the Fido™ detector by ICx Nomadics) has some of the drawbacks of IMS, requiring that target molecules reach the detecting device to interact with the fluorescing polymer. It is therefore limited to stand-off distances of ˜1-2 meters.
Accordingly, a need persists for developing detection techniques, methods and associated devices, that can quickly and accurately detect trace amounts of explosives. Furthermore, it would be advantageous to perform such detection in a fast and efficient manner (e.g., by scanning moving vehicles or cargo without the need for surface sampling or manual handling of a sample).